The present invention relates generally to recorded tape, speed-change reproducing systems, and more particularly to a system in which a tape, on which a video signal and an audio signal have been recorded, is reproduced at a speed differing from that used during recording.
In the prior art, a video signal is recorded on a magnetic tape on parallel tracks formed obliquely to the longitudinal direction of the magnetic tape.
This tape may travel at a reproducing speed which is different from the speed that was used at the time of recording. Or, the reproduced tape may stop to cause a speed-change in reproduction, such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this system, the tape speed at the time of reproduction is different from that at the time of recording. The path traced by the rotary head for reproducing the video signal differs from the path (track) traced by the rotary head during recording.
On the one hand, in a conventional video signal recording and reproducing system, recording is ordinarily, carried out on a recording medium by forming a track thereon in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats caused by the reproduction of signals from neighboring tracks due to tracking deviation of the rotary head at the time of reproduction. When a tape recorded in this manner is played back by speedchange reproduction as described above, the rotary head traces over both the track and the unrecorded guard band. When the rotary head traces over the unrecorded band, the level or strength of the reproduced signal is remarkably lowered; or it could disappear. For this reason, a noise is generated in the reproduced picture. Furthermore, since unrecorded bands are provided between the tracks in the above-mentioned system, the efficiency of the tape utilization has been poor.
In addition, there has been a system wherein the angle of inclination of the tape relative to the rotary head rotating plane is varied in accordance with the tape speed so that the rotary heads will trace accurately over the track at the time of speed-change reproduction. However, this system has a complex mechanism for varying the inclination angle of the tape, which gives rise to a high cost. It is difficult to track accurately in actual practice.
On the other hand, a system has been proposed wherein tracks are formed on a tape without gaps or guard bands between neighboring tracks. A color video signal can be recorded and reproduced without causing a beat disturbance. This system is described in the U.S. patent application Ser. No. 731,935 entitled "Color video signal recording and/or reproducing system", filed Oct. 13, 1976, by Akira Hirota and assigned to Victor Company of Japan, Ltd., the same assignee of the present invention.
In this previous system, a pair of azimuth heads have gaps which are inclined, with a certain azimuth angle, in mutually opposite directions with respect to the direction which is perpendicular to the longitudinal direction of the track. Neighboring tracks are formed in contiguous contact side-by-side without a gap or guard band therebetween. Furthermore, the phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period. The direction of this phase shifting is reversed from one track to the neighboring track. In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other. Moreover, there is no beat disturbance.
Further, another system has been previously proposed which is particularly applicable to the above mentioned system. The above described difficulties has been overcome, as described in the U.S. patent application Ser. No. 891,409 entitled "Video signal speed-change reproducing system", filed Mar. 29, 1978, by Yoshihiko Ota and assigned to Victor Company of Japan, Ltd., the same assignee of the present invention. According to this system, the tape utilization efficiency is high. Any noise bar due to a lowering of the reproduced signal strength in the reproduced picture is always located at an inconspicuous position on the picture screen. Moreover a wide speed-change range can be used.
In the apparatus to which the above system is applied, the rotational speed of the rotary head is extremely high in comparison with the tape travel speed. Even if the tape travel speed changes according to the above described special speed-change reproduction modes, the scanning speed of the rotary heads relative to the tape speed undergoes change little change. The audio signal is recorded by a stationary head on a track for audio signals formed near the edge of the tape. The audio track extends in the longitudinal direction along the tape. Thereafter, it is reproduced by the stationary head. Accordingly, in the above described speed-change reproduction mode, when the tape travels at a speed which is different from that used at the time of recording, the track for the audio signal is traced by the stationary head at a relative speed which is different from that at the time of recording.
Therefore, in the speed-change reproduction mode, the audio signal is reproduced as a signal having frequency and pitch which is different from those used at the time of recording (or normal reproduction). As a result, in the speed-change reproduction mode, the frequency, pitch, tone quality and the like change greatly from those at the time of normal reproduction. It becomes extremely hard to hear the reproduced sound, or difficult to comprehend the reproduced sound information contents.